The present invention relates to a processing method of photothermographic materials, which results in reduced in variation of photographic performance and dimensional change, and is also superior in productivity, and further to a photothermographic material and an automatic thermal processor.
In the field of printing-plate making and medical diagnosis, waste liquor produced in wet-processing of image forming material results in problems and in addition reduction of processing effluent is strongly desired in terms of environmental protection and space saving. Accordingly, a method for photothermographic materials is required which enables efficient exposure by means of a laser image setter or a laser imager and formation of black images exhibiting high resolution and clearness.
As such a technique is known a thermally developable photothermographic material which comprises on a support an organic silver salt, light sensitive silver halide grains, reducing agent and a binder, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. Morgan xe2x80x9cDry Silver Photographic Materialsxe2x80x9d in Handbook of Imaging Materials, page 48 (Marcel Dekker Inc., 1991). Photothermographic materials are stable at ordinary temperatures and after exposure to light, they are developed by heating to a higher temperature (e.g., 80 to 140xc2x0 C.). Upon heating, silver is formed through an oxidation-reduction reaction between an organic silver salt (which functions as an oxidizing agent) and a reducing agent.
Such photothermographic materials have been employed mainly as a microphotographic material and for radiographic use, and partially as a photographic material for graphic arts use. The obtained images which exhibit a relatively low maximum density (hereinafter, also denoted as Dmax) and contrast are inferior as a photographic material for graphic arts use. Recently, on the other hand, scanners and image setters employing a laser or a light-emitting diode have become popular and a photothermographic material suitable for an outputting machine and exhibiting higher sensitivity, Dmax and contrast have been urgently sought.
With regard to such a photothermographic material, a technique for increasing contrast with a contrast-increasing agent such as hydrazine derivatives is known in the art, as described in U.S. Pat. Nos. 5,545,505 and 5,545,515; and JP-A 9-90550 (hereinafter, the term, JP-A refers to an unexamined and published Japanese Patent Application).
In processing photothermographic materials, the photothermographic material is gradually heated to provide an overall uniform temperature to reduce a variation of photographic performance and a dimensional change, resulting in a slower processing speed, relative to the wet-processing system, thereby lowering productivity. Therefore, an enhancement of productivity is desired. Further, reduction of fluctuation in image density or dot percentage for use in printing plate making is also desired.
In processing photothermographic materials, increasing the speed or raising the temperature results in uneven development, leading to more fluctuation in density within the imaging area. Specifically, incorporation of a contrast-increasing agent results in such a problem. Although such contrast-increasing agent is required to improve dot quality, development stability is markedly deteriorated. Supposing a photothermographic material containing a contrast-increasing agent and giving an intended image upon developing at 120xc2x0 C. for 30 sec., for example, if it is developed at 120xc2x0 C. for 45 sec. or at 125xc2x0 C. for 30 sec., development becomes so active that unexposed areas are also developed. In the formation of halftone dots of 90% or more (so-called large dots), slightly excessive heating results in blocking of dots. In the case of halftone dots of 10% or less (so-called small dots), development proceeds so quickly that it is difficult to obtain the intended dot percentage. Thus, improvement of dot quality results in development unevenness.
PET is generally employed as a support for photographic materials. However, photothermographic materials are thermally processed at a temperature higher than the glass transition temperature (Tg) of PET and increasing the transport speed results in increased tension on the photothermographic material or further fluctuation in tension, leading to an increased dimensional change, which deteriorates reproducibility.
The present invention was achieved in response to the foregoing, and it is therefore an object of the invention to provide a processing method of photothermographic materials, thereby enabling to obtaining high contrast images without increased fogging, reducing variation of photographic performance and dimensional change, fluctuation in image density and dot percentage, and also enhancing productivity.
The object of the invention can be accomplished by the following constitution:
1. A method of processing a photothermographic material comprising the step of:
heat-developing the photothermographic material in an automatic thermal processor,
wherein the photothermographic material comprises a support, a light sensitive silver halide, an organic silver salt, a reducing agent and a contrast-increasing agent,
and wherein in the step of heat-developing, the photothermographic material is allowed to be transported at a speed of 22 to 40 mm/sec.; and the photothermographic material is allowed to pass through an atmosphere of not less than 117xc2x0 C. in not less than 10 sec., and then to pass while being brought into contact with the surface of a heating member exhibiting a surface temperature of 90 to 115xc2x0 C. or in the vicinity of the surface of the heating member;
2. The method described in 1, wherein the heating member exhibiting a surface temperature of 90 to 115xc2x0 C. is a final temperature-controlled heating member in the thermal processor;
3. The method described in 1, wherein the photothermographic material is allowed to pass through an atmosphere of not less than 117xc2x0 C. in not less than 10 sec., and then to pass within 10 sec., while being brought into contact with the surface of a heating member exhibiting a surface temperature of 90 to 115xc2x0 C., or in the vicinity of the surface of the heating member;
4. The method described in 1, wherein the thermal processor comprises a heat-developing section, the heat-developing section being provided with a napped material;
5. The method described in 1, wherein the support exhibits a thermal dimensional change under 125xc2x0 C. for 25 sec. of 0.001 to 0.04%;
6. The method described in 1, wherein the support has a thickness of 110 to 150 xcexcm;
7. The method described in 1, wherein when the photothermographic material is heated from 25xc2x0 C. to 115xc2x0 C. in 8 to 12 sec. and then heat-developed at 115xc2x0 C. in not less than 10 sec., the photothermographic material exhibits a contrast of 6 or more;
8. The method described in 1, wherein when the photothermographic material is transported in an atmosphere of a temperature of 60 to 130xc2x0 C. at a speed of 22 to 40 mm/sec. and developed for a period of 25 sec., the photothermographic material exhibits a contrast of 6 or more;
9. An automatic thermal processor for heat-developing an exposed photothermographic material comprising a heat-developing section, wherein a transport speed of the photothermographic material in the heat-developing section is 22 to 40 mm/sec. and the heat-developing section is under an atmosphere of a temperature of not less than 117xc2x0 C.; the photographic material is allowed to pass through the atmosphere of not less than 117xc2x0 C. in not less than 10 sec., and then to pass, while being brought into contact with the surface of a heating member exhibiting a surface temperature of 90 to 115xc2x0 C. or in the vicinity of the surface of the heating member;
10. The thermal processor described in 9, wherein the heating member exhibiting a surface temperature of 90 to 115xc2x0 C. is a final temperature-controlled heating member in the thermal processor;
11. The thermal processor described in 9, wherein the photothermographic material is allowed to pass through an atmosphere of not less than 117xc2x0 C. in not less than 10 sec., and then to pass while being brought into contact with the surface of a heating member exhibiting a surface temperature of 90 to 115xc2x0 C. or in the vicinity of the surface of the heating member within 10 sec.;
12. The thermal processor described in 9, wherein the thermal processor comprises a heat-developing section, the heat-developing section being provided with a napped material;
13. A method for processing a photothermographic material comprising a support having thereon a light sensitive silver halide grains, a reducing agent and a contrast-increasing agent by the use of a thermal processor, wherein in the thermal processor, a transport speed is 22 to 40 m/sec. and a final temperature-controlled heat source in the processing step exhibits a temperature of 90 to 115xc2x0 C.;
14. A method for processing a photothermographic material comprising a support having thereon a light sensitive silver halide grains, a reducing agent and a contrast-increasing agent by the use of a thermal processor, wherein the thermal processor comprises the steps of
transporting the photothermographic material in an atmosphere of 117xc2x0 C. or higher at a transport speed of 22 to 40 mm/sec for a period of 10 sec. or longer, and then
bringing the photothermographic material into contact with the surface of a heating member exhibiting a surface temperature of 90 to 115xc2x0 C., and
the photothermographic material is brought into contact with the surface of the heating member within 10 sec. after passing through the step of transporting in an atmosphere of 117xc2x0 C. or higher for a period of 10 sec or longer;
15. A method for processing a photothermographic material comprising a support having thereon light sensitive silver halide grains, a reducing agent and a contrast-increasing agent by the use of a thermal processor, wherein in the thermal processor, a transport speed is 22 to 40 m/sec. and a heat-developing section is provided with a napped material; and in 13, 14 or 15 described above, the support of the photothermographic material exhibits a thermal dimensional change at 125xc2x0 C. for 25 sec. of 0.001 to 0.045 and a thickness of 110 to 150 xcexcm;
16. A method for processing a photothermographic material comprising a support having thereon a light sensitive silver halide grains, a reducing agent and a contrast-increasing agent in a thermal processor, wherein in the thermal processor, a transport speed is 22 to 40 m/sec. and a final temperature-controlled heat source in the processing step exhibits a temperature of 90 to 115xc2x0 C.;
17. A method for processing a photothermographic material comprising a support having thereon light sensitive silver halide grains, a reducing agent and a contrast-increasing agent by the use of a thermal processor, wherein in the thermal processor, a transport speed is 22 to 40 m/sec. and a heat-developing section is provided with a napped material; and
18. the method described in 16 or 17, wherein the support of the photothermographic material exhibits a thermal dimensional change at 125xc2x0 C. for 25 sec. of 0.001 to 0.04%.
Assuming that fluctuations in image density caused by an increase in processing speed are ascribed to a cooling history after development, the inventors of the present invention found that development reaction of an organic silver salt as a silver source scarcely proceeds at a temperature lower than 115xc2x0 C. and therefore the reaction could be stopped by changing to this temperature. Thus, the invention described in 1 above was achieved by controlling the region of changing from the developing temperature to a temperature lower than 115xc2x0 C.
In heat development of a photothermographic material in which an intended developed image can be obtained by heating at not less than 117xc2x0 C. for a period of not less than 10 sec., temperature control is indispensable to obtain the intended image. In the commonly known thermal processing process, various attempts have been made to prevent development unevenness caused by non-uniform temperature wit respect to the step of raising a photothermographic material from room temperature to a developing temperature. Although temperature control prior to development is important, it was proved that the step of lowering the temperature after development greatly affects photographic performance, that is, photographic performance was markedly variable by temperature-lowering pattern after heat-developing step, i.e., after passing through an atmosphere of 117xc2x0 C. or higher. Thus, it was found that fluctuation in density of developed portions, fluctuation in dot percentage of halftone dot images, linearity and reproducibility of dimensional change can be improved by bringing the photothermographic material into contact with a member exhibiting a surface temperature of 90 to 115xc2x0 C. after the developing step at 117xc2x0 C. or higher.
Further, considering that increasing the transport speed increases tension applied to a photothermographic material, tension applied to a photothermographic sheet is different between the center and side portions and tension is also different between the transport positions, uneven development and dimensional change were improved by using a napped material in the developing section to make uniform tension applied to the photothermographic material. The invention described in 2. above was thus achieved.
The present invention found pronounced effects in improvements of density unevenness, linearity and reproducibility of dimensional change.